The invention relates to a furnace having
a firebox,
at least one discharge device disposed at the lower end of the firebox for combustion chamber ash, and
a conveyor disposed below the discharge device for the receipt and removal of the discharged ash in a dry state.
The combustion chamber ash, which is withdrawn at the bottom from the firebox, is obtained at a temperature of 800 to 1200xc2x0 C. One originally allowed the combustion chamber ash to fall into a water bath, from which it was withdrawn via the conveyor. With modern low NOx furnaces, the ash quality has changed such that the subsequent transfer process would be problematic due to the absence of an ability to remove water from the ash. In addition, there were storage and removal problems.
On the basis of this background, a dry ash removal process was developed with which the problem of removing water from the combustion chamber ash was eliminated. In addition, the dry ash can be better reused or, after appropriate processing, can even be mixed with the filter ash. In this way there results a uniform removal mode for the entire ash of the bituminous coal furnace.
The known dry ash removal process is operated with a bituminous coal furnace that is described in a prospectus of the U.S. American company United Conveyor Corporation from the year 1997. The ash is collected on screens or grids, and is introduced by batches into a vacuum transfer system.
The object of the invention is to improve the cooling of the combustion chamber ash as well as the handling, removal and utilization thereof.
To realize this object, the initially mentioned furnace is inventively characterized in that
the conveyor is embodied as a continuous-flow conveyor, and
a device for cooling the ash by means of air is provided.
It is proposed pursuant to an important further development of the invention that the continuous-flow conveyor be embodied as a vibrating conveyor and have a vibrating trough that is open toward the discharge device.
Vibrating conveyors are extremely sturdy, which is of great significance with regard to the abrasive characteristics of combustion chamber ash. In addition, such conveyors have high conveying capacities and readily permit not only a discontinuous as well as a continuous operation, in other words, a very variable and effective dry ash removal process.
Above everything else, vibrating conveyors can be combined with a very effective air cooling. Thus, the temperature of the combustion chamber ash can effectively, i.e. rapidly, be reduced to low values during the removal.
In this connection, it is to be emphasized that the inventive means for the removal and cooling of the combustion chamber ash are straightforward, economical and reliable in operation.
The invention is primarily usable with bituminous coal furnaces, although it is also usable on other furnaces, such as lignite or brown coal furnaces, refuse incinerators, etc.
Pursuant to a further development of the invention, it is proposed that the base of the vibrating trough be provided with nozzle openings for the cooling air. The cooling air passes through the ash deposited in the vibrating trough and can then pass into the firebox, in which it is utilized as preheated air for combustion. Alternatively, or in addition thereto, there is the advantageous possibility of providing the vibrating trough with lateral nozzle openings for the cooling air. This leads to a very intensive cooling of the upper surface of the ash deposit in the vibrating trough and of the ash-particles that have just dropped down. Also in this case there results preheated combustion air for the firebox. Finally, there is the possibility of also providing the discharge device with nozzle openings for the cooling air. Thus, the combustion chamber ash is already cooled in the counter flow prior to being deposited upon the vibrating conveyor, which leads to a very intensive cooling and preheating of the air for combustion.
The introduction of cooling air as preheated combustion air into the lower region of the firebox has an additional advantageous effect, namely an afterburning of the combustion chamber ash. This improves the combustion of the fuel (bituminous coal) furnace and reduces the amount of combustion chamber ash that is produced.
Depending upon the operating conditions, the underpressure that exists in the firebox can be sufficient to draw in the cooling air through the individual nozzles. However, under certain circumstances it is also advantageous to connect at least some of the nozzle openings to a blower. This can increase the throughput of cooling air and primarily leads to an improved controllability of the cooling process. The danger that the nozzle openings become clogged is also reduced.
In addition to the above discussed direct cooling of the combustion chamber ash, pursuant to a further development of the invention an indirect cooling is also proposed, whereby the vibrating trough is combined with an air receiver that is connected to the firebox. The cooling air thus passes against the underside of the trough and withdraws heat from the combustion chamber ash without coming in to contact with the latter. Since the air receiver is connected to the firebox, there again results preheated air for combustion.
It is readily possible within the scope of the invention to combine the indirect cooling of the combustion chamber ash with the direct cooling.
With the indirect cooling, it is advantageous to provide the underside of the vibrating trough with cooling ribs or the like in order to increase the heat transfer in a controlled manner.
Also with the indirect cooling the underpressure in the firebox can suffice to draw the cooling air through the air receiver. Alternatively, there exists the possibly more advantageous possibility of connecting the air receiver to a blower. The advantages relative thereto were already described in conjunction with the direct cooling.
To the extent that a blower is used, whether with the indirect or with the direct cooling, such a blower is preferably the fresh air blower that supplies combustion air to the firebox. A portion of this combustion air is thus branched off as cooling air and is introduced into the combustion chamber as preheated air, and in particular either directly or also after being returned to the combustion air stream.
Pursuant to a further development of the invention, it is proposed that the discharge device be provided with an angled-off outlet and that the vibrating conveyor is disposed below the angled-off outlet. This configuration effects a considerable contribution to the cooling process since the vibrating conveyor is not located in the direct radiation range of the firebox. This improves the cooling, i.e. reduces the required cooling capacity. In addition, it enables the use of fewer special or high-grade materials.
Pursuant to a further advantageous feature, the discharge device is provided with closure dampers that offer the possibility of delivering the combustion chamber ash to the vibrating conveyor in a batch-wise manner. Frequently, however, one will prefer a continuous ash discharge. In this case, the closure dampers then offer the possibility of temporarily storing the ash if brief disruptions occur in the region of the vibrating conveyor or if minor repairs or maintenance work must be carried out. This eliminates the need for having to shut down the furnace.
The main area of application of the invention is for bituminous coal furnaces in power plants for the generation of steam.